Electric system for producing intermittent or flashing light



Sept. 2, 1947. H. E. EDGERTON 2,426,602

ELECTRIC SYSTEM FOR PRODUCING INTERMITTENT OR FLASHING LIGHT Filed Nov. 12, 1941 fjw Y l0 I 4+ swwwu 3& as

Patented Sept. 2, 1947 UNITED STATES PATENT OFFICE ELECTRIC SYSTEM FOR- PRODUCING IN- TERMITTENT OR FLASHING LIGHT The present invention relates to electric systems, and more particularly to systems for producing intermittent or flashing light. Amon the applications of the invention are stroboscopes, high-speed electrical flash photography and highspeed-motion-picture photography. Electricaldischarge tubes in general use may be broadly divided into two categories: those operating principally on the thermionic principle; and those usually designated as gas-filled or gas-containing tubes. Though both these types of tubes are commonly referred to as vacuum tubes, the tubes of the thermionic type are characterized by a higher degree of vacuum, and will be referred to herein as vacuum tubes. Ther-mionic tubes operate upon the principle of a pure-electron discharge. Though usually containin some gas, the amount of gas so contained is relatively so very small that relatively very little gas ionization takes place. Tubes of this character accordingly operate under relatively high voltages and low currents, resulting from the substantial absence of gas ionization. It is, therefore, proper to distinguish thermionic tubes by this characteristic from the gas-filled or vapor, or combination of gas-and-vapor or gas-containing tubes, by referring to the latter as gas tubes.

Gas tubes contain gas or vapor or both at pressures sufficiently high so that electrons, by collid- 7 ing with the gas particles, ionize them. They may, therefore, be operated at lower voltages and higher currents, rendered possible by the positive ionization of the gas or vapor particles through impact of the emitted electrons. The large currents are rendered possible by the neutralization of the space charge between the electrodes by the positive ions, and even when the electrodes are subjected to only a small potential drop. The current is carried largely by the electrons. The ions drift slowly in the space, neutralizing the space charge. The ions aid also in extracting electrons from the cathode. The electrodes of gas tubes may be non-thermionic; they may be caused to emit electrons at room temperature or by bombardment, but they may also be operated at the high temperature necessary for thermal electron emission.

In each of Letters Patent of the United States 2,181,879, issued December 5, 1939, and 2,186,013, issued January 6, 1940, there is disclosed a gaseous-discharge lamp for producing a light flash upon the discharge therethrough of a condenser. The moment of discharge of the condenser is determined by a gas-filled grid-controlled tube that is instrumental in applying a short-time highvoltage pulse to a starting electrode of the gaseous-discharge tube,

For some purposes, it is often desirable to energize the starting electrode from a vacuum tube, instead of from the gas-filled grid-controlled tube before mentioned, and an object of the invention is to provide a new and improved system of the above-described character comprising a vacuum tube for starting an electrical flash-lamp.

The use of vacuum tubes, as distinguished from the said gas-filled tubes, for controlling the operation of the condenser has usually been attended with practical difliculties. Among other factors, the conventional vacuum tubes ordinarily employed in amplifiers, oscillators and the like, owing to their relatively small cathodes and relatively large impedances, are not adapted for the passage of current surges large enough to supply the necessary current for the condenser discharge in the trip circuit.

A further object of the present invention, however, is to provide a novel circuit in which conventional vacuum tubes may be employed to produce high-voltage surges of short duration.

With these ends in view, a feature of the invention resides in operating the vacuum tube with a high plate or output voltage at the moment of the surge. This high-surge voltage appears suddenly across a coil the circuit of which is connected to the said starting electrode at the instant the current is stopped. Control of the instant of flash through the gaseous-discharge lamp is thus made positive and certain, and without the necessity for supplying an abnormally large current through the vacuum tube.

Other and further objects will be explained hereinafter and will be particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawings, in which Fig. 1 is a diagrammatic View of circuits and apparatus arranged and constructed according to one embodiment of the invention; Figs. 2, 3 and 4 are explanatory diagrams illustrating, respectively, as ordinates, the current in the coil 29 (Fig. 1) or 30 (Fig. 5) or in the plate or output circuit of the vacuum tube, the voltage across the said coil or across the vacuum tube, and the grid voltage on the vacuum tube, the time being represented. along the axis of abscissae; and Fig. 5 is a View similar to Fig. 1 of a modification,

A luminescent normally non-conductive electric flash-lamp is illustrated as of the gaseousdischarge, three-electrode type, provided with two principal internal electrodes in a lass envelope or tube 2, and a normally unenergized starting or control electrode I external thereto for rendering the lamp conductive between the cathode and the anode. Lamps 2 having more than two electrodes may obviously also be employed. The lamp 2 may be straight, as illustrated, or it may be bent into U-shape, =or twisted into spiral form, or it may have any other convenient shape. The

gas contained in the tube may, for example, be:

.mercuryvapor, argon, neon, krypton orxenon; or

the lamp may be filled with a mixture of any of y these or other suitable gases.

The internal electrodes are illustrated as a solid metal cathode i and a solid metal: anode: 6i l f as a wire twisted externally around the lamp. In 7 Fig. 5, the starting electrode I00 is indicated in more general fashion than in Fig. l. The electrodes may, of course, assume other forms thanthose illustrated. The cathode 4 may; for example, as illustrated in the said Letters Patent, be constituted of .a pool of mercury, andthe starting electrode I00 may be in the fiornr of external metal band opposite to the meniscus of the mercury.

The cathode i and: the anode 6 are shown con'-- nected in the output circuit of the tube 2, directly across a maindischarge condenser 255,. by means of WiIG'COIIdUClJOI'S'fi and I0.- The electrical flashlamp- 2: is flashedby the discharge of this condenser therethrough after it has'become charged,

through a current-limiting charging impedance 35, from any suitable source of'direct-ourrent' energy, such as a battery 102-. Theimped'ancefit'is usually a combination of resistance and inductance. The quantityof light flashed through the 4 shown so connected into circuit; in Fig. 5, the anode 52 is shown connected to the coil 30, which constitutes an auto-transformer, by a variable ta 28. The use of this auto-transformer 30, in substitution for the inductance coil 29, provides for impressing a lower voltage on the plate 52' of the tube Mi than for the starting circuit, The output circuit of the tube I isconnected to the electrode I00 by a conductor 36.

In Fig; 1", the grid 50 is shown connected to the resistor 3| in series with a variable resistor I42. The connection is through a tap 34, and the resistor is supplied with energy from. a battery IE3; in order that the resistor 3| may serve as a bias potentiometer.

connections are provided so that the resistor shall lamp- 2 is determined bythe amount of energy in the condenser 26 and by circuit conditions.

To'cause the flash-lamp '2 to start, thes-tarting electrode I00 is shown excitedfrom aninductance coil or wind-ing'29 (Fig.1) or 30 (Fig. 5), in circuit with a vacuum trigger tube M0. The vacuum tube I is designed'to cut the coil 29 off suddenly. The operation ofthe vacuumtube I llito cut elf the current in the coil 2-9-may' be effected in any desired manner;- as by means of a switch 32, shownin' Fig. 1, or agrid-controlled gas-filled tube I30, illustratedin Fig. 5 and described hereinafter. The switch 32 may be manipulated byhand; but if periodic flashes are desiredthrough the lamp 2; as for stroboscopi'c purposes, the switch 32 maybe replaced byaperiodically op erating contact-making-and breaking apparatus, such as a commutator or relay. The current carried by the switch 32'ls usuallynegligible, since stillserve, in the system of Fig. 5, as a potentiometer; Theconnections of Fig. 5 are more fully described hereinafter,

Th negative bias surge imposed, uponv the grid 50 is very large, much larger'than is the case with vacuum tubes as ordinarily operated. This may, indeed, be termed anabnormal use of the vacuum tube. I40, under conditions of a very high plate potential, which requires a, very'large grid voltage to obtain cut-off of the plate current. Withvalues hereinafter given, avoltage of 100 volts'on the battery I0! may yield an: output voltage of 10,000 across the coil '20-".

According to this abnormal use of the vacuum tube I40, current normally flows through its. output circuit, including the inductance 20 or 30,-the energy being supplied from the battery 10L *'At the instant that the grid 50 becomes subjected to a suitable stimulus, however, as when the switch 32 0f. Fig. 1 becomes closed, or the gridcontrolled rectifier I30 of Fig. 5' becomes operative, the current normally flowing in the circuit of the vacuum tube M0 is suddenly out 01f by the tube I50. The consequent rapid change-of cur rent in the output circuit ofthe tube I40 and ,the coil 29= or 30' therein results in applying accurately, reliably andrapidlya sudden positive high-voltage pulse, through the conductor 30 on the grid I-00 of the flash-tube 2. The energy for producing this high-voltage pulse comes from inductively stored energy in the coil 29 or 30.

The high-potential-pulse gradient that is thus established accurately, reliably and rapidly between the starting electrode I00 and the cathode- 4 is indicated by the left-hand halt-cycle peak surge 31 shown in the graph of Fig. 3. Because the switching is effected in the grid circuitofthe tube I40.

The windingZ-Q- or 30 is shown connected, in series With-a source of direct-current energy, suchas a battery Ill-I, in-the power output or controlinput or plate circuit of the vacuum tube Mil, between the cathode 40 and the plate oranode 52'. This power output circuit may be traced from the cathode 48, through the tube I 40', to the anode: 52, through the coil 2-9 or 30, and the battery I01, back-to the-cathode 48; The input 'orgrid circuit of the vacuum tube I40 may be traced from the cathode 48;, through a. control electrode or grid 50, and a' resistor 3-I, back toi-the cathode 48; The switch. 32, the grid-controlled rectifier I30, or other mechanism for operating the vacuum. tube I430, operates by producing a negative surge upon of this surge, a flash is produced momentarily through the lamp 2, between itscathode 4 andanode 6.

The method just described is also efiective for starting gas-filled tubes for rectifier-s er inverters as well as for light-flash sources. In the case of tubes having mercury-pool cathodes 4,.the

pulse on the starting electrode I00 causes a source The grid 50 is at first positive; as: shown at 39,

or, perhaps, slightly negative by an amount de-' termined by the setting ofthe bias. potentiometer 3!. If grid current flows: in the grid or input circuit, the series resistor I42 also controls the:

Though the resistor Hi2 and V the battery I 03 are omitted from Fig. 5, other initial bias, and. thereby the plate current through the coil 29 or the auto-transformer 30. The initial plate current is proportional to the highvoltage pulse, the magnitude of which may be conveniently varied to suit desired conditions by adustment of the potentiometer 3 I, or the resistor I42, or both. The cut-ofi point 4| of the curve of Fig. 4 is directly below the point 43 of the curve of Fig. 2 where the curve of Fig. 2 starts to become positive. That point determines the tube cut-01f bias.

The switch 32 may be employed also to impress a continuous negative bias on the grid 50. It is preferred, however, to employ a condenser type of circuit, as illustrated in Fig. 1, with a condenser 59, in parallel with a leak resistor I43, connected between a battery I04 and the grid 50 through the switch 32. The grid 50 is connected to one side of the switch 32 through the condenser 59. The other side of the switch 32 is connected through the battery I04 to the cathode 48. This condenser-type of circuit automatically permits the plate current, after each flash, to build up for the next flash. As the condenser 59 becomes charged from the battery I04, the bias varies exponentially with time, as illustrated in Fig. 4. The time constant is determined by the size of the capacitor 59 and the resistor I 42. A correction is necessary if the resistance of the potentiometer is comparable in value with resistor I42.

The plate current in the vacuum tube I40 and the inductance 29 decreases to zero in a very short interval of time, as shown in Fig. 2. The energy that was stored in the magnetic field of the inductance of the coil 20 now becomes stored in the distributed capacityof this coil, the tube I40 and their associated circuit. Since this capacity is small, the voltage will be high.

The following numerical example illustrates the order of magnitude of the quantities that have been used experimentally. A coil 29 was used having 15,000 turns, an outside diameter of 2 inches and a length of 4 inches, its inductance being about one henry. The current through this coil 29, before cut-01f, was about 0.2 ampere. Equating the stored energy in the magnetic field to the stored energy in the electrostatic field, the voltage obtained when the current was suddenly reduced to zero Assuming the capacity to be 400 X farads, the peak computed plate voltage, as plotted in Fig. 3, is 10,000 volts. The frequency of oscillation is determined by the circuit constants:

f= m =about 4,000 cycles Usually the frequency is higher than given in this illustrative example.

The damping of the oscillation can be increased by using an inductance coil 29 of high resistance, or by using a resistor (not shown) across the terminals of this coil 29.

The grid-voltage power supply I04 must be enough to cut oiT the plate current with the highsurge voltage on the plate. In the example just given, assuming an amplification factor of 10, the necessary bias will be about or 1,000 volts.

The resistor S43 is used to discharge the capacitor 59 between operations. It is high enough in value so as not to influence appreciably the charging cycle.

Fig. 5 illustrates a relaxation oscillator with the gas-filled grid-controlled tube I30 beforementioned. The tube I30, may, for example, be a thyratron, having a cathode 38, an anode 42 and a grid or control electrode 40. The relaxation oscillator may, however, employ vacuum tubes instead of gas-filled tubes to generate the sudden negative voltage on the grid 50. This oscillator may be either of the self-driven or externally driven type.

A small condenser 27, charged from a battery or other direct-current source I05, operates to trigger the tube A30 to effect flashing of the lamp 2 when the potential of the grid 40 is raised to a predetermined critical value with respect to the cathode 38. One side of the condenser 2'l is shown connected to the grid 50 through a coupling condenser 44. The other side of the condenser 27 is shown connected to the oathode 40.

A bleeder resistor 33, in parallel with the battery 505, allows a smallcurrent to.flow, in order to maintain the proper voltage bias upon the grid 40. The grid 40 is connected so that it is negative with respect to the cathode 38 during most of the cycle. Frequency adjustment is obtained by the use of a variable tap on the resistor 33, or by means of surges or an alternating voltage applied to a transformer 54. The tap on the resistor 33 may be employed to obtain self-osciliation of the circuit of the tube I30. In that event, the separate oscillator 64, of course, will not be needed.

I When the grid 40 becomes positive with respect to the cathode 38, the tube I30 becomes conductive, permitting the condenser 21 to discharge therethrough. The potential of the grid 50 is thus raised to a high negative value, with respect to the cathode 48, producing a high potential upon the starting electrode I00, and producing a flash in the lamp 2.

Further modifications will occur to persons skilled. in the art, and all such are considered to fall within the spirit and scope of theinvention, as defined in the appended claims.

What is claimed is: p

1. An electric system having, in combination, a gaseous-discharge tube that is normally nonconducting when not in operation, a vacuum tube, means for normally passing current through the vacuum tube when the vacuum tube is in operation, means for stopping the flow of current through the vacuum tube, means controlled by the stoppage of current through the vacuum tube for rendering the gaseous-discharge tube conducting, a condenser, means for charging the condenser, and means for discharging the condenser through the gaseous-discharge tube when the gaseous-discharge tube becomes conducting.

2. A flash-producing electric system having, in combination, a luminescent gaseous-discharge lamp that is normally non-conducting when not in operation, a vacuum tube, means for normally passing current through the tube when he i e i i eeere i h; me or-s i he flow of current tube; means controlled by the stoppage of current through the tube for rendering the lamp conducting, a condenser, means for charging the condenser, and means for discharging the condenser to produce a memehtary lumines nt fle h in e m when the lamp becomes conducting.

3, A, flash-producing electric system having, in combination, a luminescent gaseous-discharge am that i no ma hon-t n st he h t in operation, a vacuum tube having an anode, a cathode and a'control electrode that is normally unenergi zed when the tube is in operation, an input circuit in which the cathode and h 99 41 19 l tr de the QQPHfi a output circuit in which the cathode and the anode are connected, means for normally passing current in the output circuit when the tube is in operation, means connected with the input circuit or ener i in he ee r le t od to step. the flow of current in the output circuit, means controlled by the stoppage of the flow of currentin he out cir er rende i h a p onlhet ha e e ndehs n mea for e ei e the ee de se she r a s. o discharging t q filf .11 is We am t qq a m m h e luminescent ilash in the lamp when the lamp becomes conduct-ing.

lfA flash-producing electric system having, in combination, a luminescent gaseous-discharge lamp that is normally non-conducting when not operation, a vacuum tube having a control electrode that is normally ineffective when the tube is in operation, means for normally passing current through the tube when the tube is in operation, means for rendering the control electrode effective to stop the flow of current through the tube, means controlled by the stoppage of the flow of current thro gh the tube for rendering the lamp conducting, a condenser, means for charging the condenser, and means for discharging the condenser through the lamp to produce a momentary luminescent flash in the lamp when the lamp, becomes conducting.

5- A ie hredheihs e eetri s st m n in combination, a luminescent gaseous-discharge lamp that is normally non-concludin When not in operation, a vacuum tube operating upon t Pr p e of a sure-ele tro d e rs h inductance, means controlled by the tube for storing energy in the inductance, means controlled by the energy stored in the inductance for rendering the lamp conducting, a condenser, means for charging the condenser, and means for discharging the condenser through the lamp to produce a momentary luminescent flash in the lamp when the lamp" becomes conducting.

6. An electric system having, in combination, a gaseous-discharge tube that is normally nonconducting when not in operation, a vacuum tube, means for normally passing current through the vacuum tube when the vacuum tube is in operation, means for stopping the flow of current through the vacuum tube, an inducttime: e s e ht elled by t e ppa e f h flow of current through the vacuum tube for storing energy the inductance, means conle b t en r y s ereri in h inductance for rendering the gaseous-discharge tube conet ih eh ehser mea s for a n the eeh leheh an i-Q disch n e den er thre ht e sese h li e r t b w the gaseous discharge tube becomes conductmg.

7. A flasheproducing Telectricsystem having, in combination, a luminescent gaseousrdischarge lamp that is normally non-conducting when not in operation, a, vacuum tube, means for normally passing current through the tube when thetube is in operation, means for stopping the flow of current through the tube, an inductance, means controlled by the stoppage of the flow of current through the tube for storing energy in the in-.

ductance, means controlled by the energy stored in the inductance for rendering the lamp conducting, a condenser, means for charging the control electrode that is normally ineffective when the tube is in operation, means for nor: mally passing current through the tube when the tube is in operation, means for, rendering the control electrode effective to stop the flow of current through the tube, an inductance, means controlled by the stoppage of. the, flow of current through the tube for storing energy in the inductance to render the lamp conducting, h hei h er means for cha in th con ns r, and means for discharging the condenser through the lamp to produce a momentary luminescent flash in the lamp when the lamp becomes conducting.

9. A flash-producing electric system having, in combination, a luminescent gaseous-discharge lamp that is normally non-conducting when not in operation, the lamp having at least tWo prin-, cipal electrodes and a control member associated with one of the principal electrodes for rendering the lamp conducting, a condenser, means for charging the condenser from asource of energy, a

vacuum tube, means for normally passing current through the tube when the tube is in'oper ation, means for stopping the flow of current through the tube, and means controlled by the connected to the anode and the cathode, means i for charging the condenser from a source of energy, a vacuum tube,'means for normally passing current through thetube when the tube is in operation, means for stopping the flow of current through the tube, and means controlled by the stoppage of the flow of current through the tube for energizing the starting electrode to render the lamp conducting, thereby to effect a discharge of the condenser between the cathode and the anode to produce a luminescent flash through the lamp.

11. An electric system having, in combination, a gaseous-discharge tube that is normally none conducting when not in operation, the tube having at least two principal electrodes and a control electrode for rendering the tube conduct.-

ing, a vacuum tube having an input circuit and an output circuit, an inductance in the output circuit, means for normally passing current in the output circuit when the vacuum tube is in operation, means connected with the input circuit for energizing the control electrode to stop the flow of current in the output circuit, and means controlled by the stoppage of the flow of current in the output circuit for storing energy in the inductance.

12. A flash-producing electric system having, in combination, a luminescent gaseous-discharge lamp that is normally non-conducting when not in operation, the lamp having an anode, a cathode and a starting electrode for rendering the lamp conducting that is normally unenergized when the lamp is not in operation, a condenser connected to the anode and the cathode, means for charging the condenser from a source of energy, a vacuum tube having an input circuit and an output circuit, an inductance in the output circuit, means for normally passing current in the output circuit when the tube is in operation, means connected with the input circuit for stopping the flow of current in the output circuit, and means controlled by the stoppage of the flow of current in the output circuit for storing energy in the inductance to energize the starting electrode to render the lamp conducting, thereby to effect a discharge of the condenser between the cathode and the anode to produce a luminescent flash through the lamp.

13. A flash-producing electric system having, in combination, a luminescent gaseous-discharge lamp that is normally non-conducting when not in operation, the lamp having at least two principal electrodes and a control electrode for rendering the lamp conducting, a vacuum tube, means for normally passing current through the tube when the tube is in operation, a gridcontrolled gaseous-discharge device for stopping the flow of current through the tube, means controlled by the stoppage of the flow of current through the tube for energizing the control electrode, means controlled by the energized control electrode for rendering the lamp conducting, and means for producing a momentary luminescent flash in the lamp upon the lamp becoming conducting.

14. An electric system having, in combination, a gaseous-discharge tube that is normally nonconductin when not in operation, a vacuum tube having an anode, a cathode and a control electrode that is normally unenergized when the vacuum tube is in operation, an input circuit in which the cathode and the control electrodeare connected, an output circuit in which the cathode and the anode are connected, the output circuit having an inductance, means for normally passing current in the output circuit when the vacuum tube is in operation, means connected with the input circuit for energizing the control electrode to stop the flow of current in the output circuit, means controlled by the stoppage of current in the output circuit for storing energy in the inductance to render the gaseous-discharge tube conducting, a condenser, means for charging the condenser, and means for discharging the con-. denser through the gaseous-discharge tube when the gaseous-discharge tube becomes conducting.

15. A flash-producing electric system having, in combination, a luminescent gaseous-discharge lamp that is normally non-conducting when not in operation, the lamp having an anode, a cathode, and a control electrode, a vacuum tube hav- 10 ing an anode, a cathode and a control electrode that is normally ineffective when the tube is in operation, the vacuum tube operating upon the principle of a pure-electron discharge, an input circuit connected between the cathode and the control electrode of the tube,tan output circuit connected between the anode and the cathode of the tube, an inductance connected in the output circuit, means controlled by the tube for storing energy in the inductance, means controlled by the stored energy for transmitting an electric impulse to the cori tirol electrode of the lamp to render the lamp conducting, a condenser connected to the cathode and the anode of the lamp, means for charging the condenser, and means for discharging the condenser through the lamp to produce a momentaryluminescent flash in the lamp when the lamp becomes conducting.

16. An electric system having, in combination, a gaseous-discharge tube that is normally nonconducting when not inoperation, the tube having an anode, a cathode and a control electrode, a vacuum tube having an anode, a cathode and a control electrode that is normally ineffective when the vacuum tube is in operation, an input circuit connected between the cathode and the control electrode of the tube, an output circuit connected between the anode and the cathode of the tube, means for normally passing current through the output circuit when the vacuum tube is in operation, means connected withthe input circuit for rendering the normally ineffective control electrode effective to stop the flow of current through the output circuit, means controlled by the stoppage of the flow of current through the output circuit for transmitting an electrical impulse to the control electrode of the gaseous-discharging the condenser, and means for discharging the condenser through the gaseous-discharge tube when the gaseous-discharge tube becomes conducting. I V

1'7. A flash-producing electric system having, in combination, a luminescent gaseous-discharge lampthat is normally non-conducting when not in operation, the lamp having an anode, a cathode and a control electrode, a vacuum tube having an anode, a cathode and a control electrode that is normally ineffective when the tube is in operation, an input circuit connected between the cathode and the control electrode of the tube, an output circuit connected between the anode and the cathode of the tube, means for normally passing current through the output circuit when the tube is in operation, means connected with the inputlcircuit for rendering the normally ineifective control electrode effective to stop the flow of current through the output circuit, means controlled by the stoppage of the flow of current through the output circuit for transmitting an electrical impulseto the control electrode of the lamp to render the lampfconducting, a condenser connected to the cathode and the anode of the lamp, means for charging the condenser, and means for discharging the condenser through the lamp to produce a momentary luminescent flash in the lamp when'the lamp becomes conducting.

18.1An electric system having, in combination,

a gaseous-discharge tube that is normally nonconducting when not in operation, the tube having an anode, a cathode and a control electrode, a vacuum, tube having an anode, a cathodeand a control electrode that is normally ineffective great-o2 11 when the vacuum tube is in operation, an-input circuit connected between the cathode and'the control electrode of the tube, an output circuit connected between the anode and the cathode of the tube,means for normally passing current through the output circuit when the vacuum tube is in operation, means connected with the input circuit for rendering the normally ineffective control electrode effective to stop the flow of cur rent through the output circuit, an inductance connected in the output circuit, means controlled. by the stoppage of the flow of current through the output circuit for storing energy in the inductance, means controlled by the stored energy for transmitting an electrical impulse to the control electrode of the gaseous-discharge tube to render the gaseous-discharge tube conducting, a condenser connected to the anode and thecathode of the gaseous-discharge tube, means for charging the condenser, and means for dischar ing the condenser through the gaseous-discharge tube when the gaseous-discharge t'ub'e becomes conducting.

19. A fiash-producingelectric system having,

in combination, a luminescent gaseous-discharge lamp that is normally non-conducting when not in operation, the lamp having an anode, a cathode and a control electrode, a vacuum tube having an anode, a cathode and a control electrode that is normally ineffective when the tube is in operation, an input circuit connected between the cathode and the control electrode of the'tube, an output circuit connected between theanode and the cathode of the tube, means for normally passing current through the output circuit when the tube is in operation, means connectedwith the tary luminescent flash in the lamp when the lamp becomes conducting.

20. A flash-producing electric system having, in;

combination, a luminescent gaseous-discharge lamp that is normally non-conducting when not in operation, the lamp having an anode, acathode and a starting electrodefor rendering the lamp conducting that is normally unenergized when the lamp is not in operation, a condenser connected to the anode and the cathode, meansfor charging the condenser from a source of ener y, a normally conducting vacuum tube operating upon the principle of a pure electron discharge, an inductance, and means controlled by the tube for storing energy in the inductance to energize the starting electrode to renderthe lamp con ducting, thereby to efiect adischarge oi the condenser between the cathodejand the anode to produce a luminescent flash through the lamp.

21. A flash-producing electric system having,in

combination, a luminescent gasequs discharge lamp that is normally non-conductingvvhennot in operation, the lamp having at least two prin cipal electrodes. and a control electrode for ren' de in he am con u n a va l m 213 9691 5 erating upon the principle of a'pure-electron discharge,'ineanscontrolled by the tube for storing energy, a grid-controlled gaseous-discharge de- 'vice fo'r controlling the stored energy to energize the control electrode, thereby to renderthe'lamp conducting, and means for producing a momentary luminescent flash in the lamp when the lamp becomes conducting. r

22. A stroboscope having, in combination, a gaseous-discharge tube having an anode, a

cathode and a starting electrode, a condenser connected between the anode and the cathode, means for charging the condenser, a normally conducting vacuum tube connected in circuit with the cathode and the starting electrode, the vacu um tube operating upon the principle of a pure I electron discharge, and means for intermittently opening and closing the circuit to render the circuit intermittently eiiective to energize the'startingelectrode intermittently and thereby to 'pro- I duce intermittently a source of electrons at the cathode, whereby the condenser will become enabled to discharge intermittently between the cathode andthe anode to produce intermittent flashes of light. I t

23. An electric system having, in combination, agaseous-dischaige tube that is normally nonconducting when not in operation, a vacuum tube operating upon the principle of a pure-electron discharge, an inductance, means controlled by the vacuum tube for storing energy in the inductance, means controlled by theenergy stored in the inductance for rendering thegaseous-discharge tube conducting, a condenser, means for charging the condenser, and means for discharging the condenser through the gaseous-discharge tube when the gaseous-discharge tube becomes theprinciple of a purerelectron discharge.

25, In combination, a gaseous-discharge tube that; is normally non-conducting when not in operation, the tube having an anode, acathode and a control electrode for rendering the tube V conducting; a vacuum tube ,Oprating upon the principle of a pure electron discharge,.rne'ans controlled by the vacuumtube fQIStOIlIlgEXlQIgY,

means controlled bythe stored energy for energizi'n'g the ,control electrode to render the aseous-di ar t be. onduc n a ndens r. arranged t'o be charged from a source of electricity conneoted directly to the anode and the cathode, and means for discharging the condenser through the gaseous dis'charge tube when} the gaseous disohargetube becomes conducting.

combination, a rgmescent gaseopsdischarge lamptnat is normally non-conducting when not in l i nrte lamphav ee -l a t q rim cipal electrodes and a control electrode for;

j e i the. l mp c ndu ne a m m u operating upon; the principleot a pure-electron discharge me ii r ue by he tu ei sari-r n? eme ing sw ch io ni b l l fi ister ld energy to energize the control electrode, thereby to render the lamp conducting, and means for 26. A flash-producing electric systemhaving, in: o

13 14 producing a momentary luminescent flash in the Number Name Date lamp when the lamp becomes conducting. 1,904,124 Cockrell Apr. 18, 1933 HAROLD E. EDGERTON. 2,186,013 Edgerton J an. 9, 1940 2,181,879 Edgerton Dec. 5, 1939 REFERENCES CITED 5 2,327,971 Slepian Aug. 24, 1943 The following references are of record in the 2310092 Knowles 1943 file of this patent: FOREIGN PATENTS UNITED STATES PATENTS Number Country Date N 10 120,621 Switzerland June 1, 1927 2 3132 f 252,779 Great Britain June 3, 1925 496,121 Great Britain Nov. 23, 1938 2,085,100 Knowles et a1 June 29, 1937 

